Process for manufacture of glow lamps



Oct. 13, 1936. T W, CASE 2,057,183

PROCESS FOR MANUFACTURE OF GLOW LAMPS Filed July 27, 1929 Patented Oct. 13, 1936 UNITED STATES PROCESS FOR MANUFACTURE OF LAMPS GLOW Theodore Willard Case, Auburn, N. Y., assignor to Case Research Laboratory, Incorporated, Auburn, N. Y., a corporation of New York Application July 27, 1929, Serial No. 381,666

17 Claims.

This invention relates to the process of manufacture of glow lamps for sound recording and other purposes.

It is an object of this invention to provide a simple means for commercially lproducing a glow lamp of high light intensity and capable of instantaneously varying its intensity in accordance with current modulations and having a comparatively long life under normal conditions of use. In order to more fully understand the process, reference will vbe made to the accompanying drawing in which:

Figure 1 is a view of the electrode assembly of a lamp beforesealing in outer casing.

Figure 2 shows electrodes assembled in bulb in readiness for drying and evacuation. process.

Figure 3 shows a view of the lamp and connections for activating and out gassing the electrodes.

Figure 4 is a view of the lamp and circuit connections for the final steps in the process of manufacture.

Figure 5 is a sectional view of thecompleted lamp shown at right angles to the other figures.

Tungsten wires 5 and 6 are sealed in lamp press I in any well known manner. To the upper ends of wires 5 and 6 is secured with silver solder filament 3 which is to act as the cathode and may preferably be formed of a platinum strip .011 inch wide and .0005 inch thick although various sizes may be used. The strip is bent into U-shaped form in conformity with the illustration of the electrode 3 in Figure l. A nickel plate 4 supported by a tungsten wire I is sealed in press 2 as the anode in a position as shown in the drawmg.

Silver lead Wires 8, 9, and I are soldered to tungsten wires 5, 6, and 7 respectively which support the electrodes 3 and 4. In circuit with the cathode 3 and connected through leads 8 and 9 is a battery I2, ammeter I I and a variable resistance i3. Resistance adjustment is made so that a current varying from 2 to 3 amperes will heat the electrode 3 to at first a dull red heat and later to a bright red.

During the heating process calcium nitrate is applied to the filament 3 which is quickly converted to calcium oxide. The calcium compound is applied until the entire exposed portion of filament 3 is covered. It will be necessary to decrease the resistance I3 from time to time as the coating is applied as it requires more current to heat the increase cross section of filament.

Barium nitrate is then applied to the heated filament and is uniformly spread over the entire surface. Care must be taken B012 t0 @10W any compound to spatter on the nickel plate 4 as this surface is to act as the anode and must be clean.

The barium nitrate converted into barium oxide due to heating of the compound in air is applied until the filament has a total thickness of approximately .035 inch. The heating of the filament strip is continued until the nitrate is converted into oxide. f

The calcium oxide is used merely for protection as' barium nitrate has a corrosive effect upon platinum. The electrodes are then assembled in the lamp as illustrated in Figure 2. A baking furnace is then placed over the tube and the structure is baked until the temperature rises to 100 degrees centigrade during which time the coated platinum filament is disconnected from the direct current source or battery I2 and an oil pump vacuum is maintained through connecting tube I5. The furnace is shut off and the structure allowed to cool for 15 minutes. The furnace is then allowed to heat until a temperature of 200 degrees centigrade is obtained after which it is again allowed to cool for l minutes. This periodical heating and cooling is continued until a temperature of 400 degrees centigrade is obtained.

The baking process has for its purpose the volatilization of any moisture in the tube and the coated platinum strip. During the process of forming the coating on the platinum strip, considerable barium hydroxide was produced which is also decomposed by the baking process.

To eliminate any final trace of moisture, the platinum coated filament is heated by means of battery I2 connected thru resistance I3 and ammeter II. The heating currents will be of the order of 3 amperes and at the same time the bulb is pumped to a high vacuum with a mercury pump operating in conjunction with an oil pump for from fifteen to twenty minutes.

The electrodes still contain a considerable amount of gas and in order to eliminate final tracesof gas, the electrodes are connected in circuit as shown in Figure 3. Battery I2 is again used as a source for heating the filament 3. Alternating current from generator I9 is stepped up to 1200 volts by means of transformer I8. The secondary terminals of transformer I8 are connected to electrode 3 and electrode 4 respectively. A current limiting resistance I6 and a switch I1 is included in the transformer secondary circuit connection. Filament 3 is heated to. a dull red heat by means of a current from battery I2 and the high potential from transformer I 0 is intermittently applied acrossthe electrodes.

switch n is suowedw be closed only for e short period of time, say to 10 seconds. At lnrst a bright luminous discharge bluish in color is noted indicating that gas is being driven from the electrodes being treated with the high voltage alternating current. As this processis continued, the luminous discharge becomes less and less and finally a green flash appears between electrodes. At this point the electrodes are apparently de-gasiiied and the cathode electrode 3 is sufnciently activated for the next process.

The current is then disconnected and the activated coating on the nlament is foimd to be photo-electric. The .vacuum pump is shut oi! from tubel II and gas is then admitted to the bulb while the electrodes 3 and I are connected in a circuit including a source of potential of about 650 manually variable. volts in series with a resistance of about 8000 ohms.

A circuit diagram of this connection is shown in Figure 4.V The gas preferred is a combination of helium and nitrogen in the ratio of about 95 parts vhelium tol 5 parts nitrogen. The presence of lnitrogen in the bulb causes the barium oxide coating to form a compound believed to be barium nitride.

When the gas within the bulb reaches a pressure where a discharge ,starts'between the electrodes and the glow practically nils the space between electrodes I and 4. a current of about 2 to 3 milli-amperes is ilowing' and the gas admitted through tube i5 is shut off. The apparatus is permitted to run in this condition until the glow is evenly distributed over the entirecathode and the current will have risen to approximately 30 to 40 milli-amperes.

Usually the glow starts in a non-uniform manv ner and later spreads out more or less uniformly over the entire -U-shaped electrode. Wherever the filament becomes activated and glows, it will be found that the coating has turned dark brown to black. This active product` that has been formed isv at present believed to be a barium nitride compound and is photo-electrically active. I A

The voltage in the circuit is then reduced to about 370 volts through the same resistance of about 8000 ohms vand more gas is admitted to thev bulb until a current of approximately 18 milliamperes is vflowing in the plate circuit. The negative glow under these conditions will be found closely surrounding the cathode and theglow is substantiallyl lavender in color and separate from theanode glow which is quite pink incolor on the surface of the anode. The tube is then sealed of! from the connecting tube Ii and is complete as lfaras the manufacturing process is concerned.

The activated lcoating substantial photo-'electric character and the entire combination produces alight of high actinic value. The pressure which I have found in prac- Y tice to -be preferable is' approximately ll5 to 25 millimeters of mercm'y although a fairly wide. range is possible between andl 4 0' millimetersV of mercury, the importantieature beingthat the pressure is such asto maintain the glow medium tightly on the-surface of the cathode.

. The electrodes 3 and l 'are preferably arranged in-close relation as for instance about 'one quarter of an inch apart although` considerable variation is possible.

I claim:

1. In the process of producinga glow lamp com- 75 prising connectinga high d irct current potential on Athe cathode has a between un electrodes. ne of which u coated, ed-

Y mitting a gas containing nitrogen until a glow' covers the space between the electrodes. then allowing the glow to continue until the coated electrode has been activated, and finally admitting more gas so that a concentrated lavender glow is produced about the cathode.

- k2. In the process of producing a glow lamp comprising connecting a high direct current potential between the electrodes, one of vwhich is coated. admitting a gas oomposedof approximately 95 per cent helium and 5 per cent nitrogen until a glow covers the space between the electrodes, then allowing the glow to continue until the coatedy electrode has been activated, and

finally admitting more.` gas so that a concentrated glow is produced about the cathode.

3. Inthe process of producing a glow lamp comprising connecting a high direct current potential between the electrodes, one of which is coated, admitting a gas containing nitrogen until a glow covers the space between the electrodes, then allowing the .glow to continue until the coated electrode sends out an intense bluish glow in the 'form of streamers. throughout its entire length, and ilnally admitting more gasv so that a concentratedlavender glow 'is produced about the cathode.

4. In the processof producing a glow lamp comprising coating an electrode with a. calcium compound and then with another alkalineearth materiaL converting said material into the oxide,

activating said coating with a source of high comprising an alkaline earth material, converting sa'id material into the oxide, activating said coating with a source of high voltage alternating current and treating saidcoating with a high voltage voltage alternating current and treating said direct current in a low pressure atmosphere inciuding nitrogen. a

'1. In the process of producing a glow lamp comprising providing anelectrode with a coating comprising analkaline Vearth oxide. activating said coating with a source of high voltage alternatin'g currentandtreating said coating with a high voltage direct current in a low pressure atmosphere including nitrogen.

8. The process of producingv a glow lamp comprising a bulb and anode and cathode electrodes therein which consists in providing the cathode with a coating of a calcium compound and'thenwith a coating of another alkaline earth oxide andjactivating said coating by the passage of an electriccurrent while the electrodes are surroundwith a coatingof a calciumcompound and then with a coating ofv barium oxide" and activating said coating by the passage of an electric current while the electrodes are surrounded' by an atmosphere of gas including nitrogen forming thereby a diierent barium compound on the cathode.

10. 'I'he process of producing a glow lamp comprising a bulb and anode and cathode electrodes therein which consists in providing the cath'ode with a coating of an alkaline earth oxide and activating said coating by the passage of an electric current while the electrodes are surrounded by an atmosphere comprising substantially 95% of helium and nitrogen forming thereby a different coating material on the cathode.

11. The process of producing a glow lamp comprising a bulb and inclosed therein anode and cathode electrodes therein which consists in providing the cathode with a coating of barium oxide and activating said coating by the passage of an electric current while the electrodes are surrounded by an atmosphere comprising substantially 95% helium and 5% nitrogen forming thereby a diierent barium compound on the cathode.

12. The process of producing a glow lamp com- A prising a bulb and anode and cathode electrodes therein which consists in providing the cathode with a coating of an alkaline earth oxide, and activating said coating by the passage of an electric current while the electrodes are surrounded by an atmosphere of gas including a relatively small percentage of nitrogen, and a relatively large percentage of an inert gas having high heat radiating characteristics.

13. The process of producing a glow lamp comprising a bulb and anode and cathode electrodes therein which consists in providing the cathode with a coating of a barium oxide, and activating said coating by the passage of an electric current while the electrodes are surrounded by an atmosphere of gas including a relatively small percentage of nitrogen, and a relatively large percentage of an inert gas having high heat radiating char- I acteristics.

14. In the process of producing a glow lamp comprising connecting a high direct current potential between the electrodes. one oi.' which is coated with a barium compound, admittinga gas composed substantially of 95 percent helium and 5 percent nitrogen until a glow occurs across the space between the electrodes, then allowing the glow to continue until the coated electrode has turned in color from light gray to dark brown to black and finally admitting more gas so that at a predetermined direct current potential substantially not to exceed 400 volts a predetermined value of current will ilow between the electrodes.

15. In the process of producing a glow lamp, the steps comprising -coating a foundation member with a calcium compound which is readily converted to an oxide, converting said calcium compound to an oxide and depositing thereon, a barium compound, then surrounding the foundation member as an electrode by a glow` discharge whereby a photo-electrically activated condition is produced. Y

16. In the process of producing a glow lamp, the steps comprising coating a foundation mems ber with a calcium compound which is readily converted to an oxide, converting said calcium compound to an oxide and depositing thereon a barium compound, subjecting said barium compound to an electrical discharge to render it photo-electrically active, then introducing an inert gas into the lamp and surrounding the foundation member, as an electrode, by a glow discharge whereby the coating is further photoelectrically sensitized. I

17. In the method of producing a device having photo-electrical characteristics, the steps comprising coating a foundation member with a calcium compound which is readily converted to an oxide, converting said calcium compound to an oxide, and then providing thereon a layer of light sensitive material, and finally introducing an inert gas into thelamp and immersing the foundation member, as an electrode, in a glow discharge whereby the light sensitive surface is further sensitized.

' l'I'I-IEODORE WILLARD CASE. 

